4.2.2.4 Type of Service: RFC 791 Section 3.1

The Type-of-Service byte in the IP header is divided into three sections: the Precedence field (high-order 3 bits), a field that is customarily called Type of Service or TOS (next 4 bits), and a reserved bit (the low order bit).

Rules governing the reserved bit were described in Section [4.2.2.3].

A more extensive discussion of the TOS field and its use can be found in [ROUTE:11].

The description of the IP Precedence field is superseded by Section [5.3.3]. RFC 795, Service Mappings, is obsolete and SHOULD NOT be implemented.